I live in Natomas (with heavy clay soil), so I want to build some raised planter beds with better soil (such as loam) for growing vegetables. However, I also want to feel confident that these veggies are safe and healthy for my family to eat, and grown in clean, uncontaminated soil.
Can you suggest a good soil to use? I don't want to purchase soil-manure mix from a supply yard because who knows the history of that soil or whether the manure came from animals treated with hormones that may be residual in their waste? Is there such a thing as certified organic soil?
Also, can you recommend a height for planter boxes? I'm planning on building three boxes, each 4 by 10 feet.
Judah Grossman, Sacramento
First of all, let's consider the positive aspects of your heavy clay soil. It holds water very well; that's a plus in a semi-arid climate, say the UC master gardeners. Nutrients adhere to clay particles and thus are available for plant nourishment.
Clay also is the binding agent for the formation of soil granules that are composed of sand, silt, organic matter, minerals, air, water and microorganisms.
On the down side, clay often holds too much water and this condition leads to exclusion of air in the soil, which is detrimental to the health of plants.
Adding organic matter to a clay soil can overcome its problems and retain its advantages. By mixing in 3 to 4 inches of organic material such as compost and turning the soil to a depth of 12 inches, an ideal site for growing vegetables can be created without hauling in new dirt or building raised beds.
This kind of bed does not need a retainer of wood, stone or other materials to hold the soil. It will stay light and fluffy as long as it is not walked on.
Raised beds are usually praised for how well they drain in the spring and accommodate early planting in not-too-wet soil. The same condition can be achieved by covering sections of beds in heavy black plastic in fall to keep most of the rain out. This soil will be workable in early March for planting chard, lettuce, beets and radishes. (Most of the other vegetables should not be planted until after the ground warms in late April or May.)
Finally, this is a far less expensive way to create a vegetable garden.
Bagged garden soil sold in stores contains animal fertilizer. Thus, the soil in your yard is probably your cleanest source.
If you follow this plan, add more organic material (such as leaves, dried grass clippings, compost or straw) to your beds each fall after the crops are harvested.
Organic material including compost made from your own kitchen waste is about all the initial investment you'll need. You'll have peace of mind and save money, too.
Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties.
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